7.3.1 Fixed Frequency PWM Control

The TPS54418 device uses an adjustable fixed-frequency peak-current-mode control. The output voltage is compared through external resistors on the VSENSE to pin an internal voltage reference by an error amplifier which drives the COMP pin. An internal oscillator initiates the turnon of the high-side power switch. The error amplifier output is compared to the high-side power-switch current. When the power switch reaches the COMP voltage, the high-side power switch is turned off and the low-side power switch is turned on.

The COMP pin voltage increases and decreases as the peak switch current increases and decreases. The device implements a current-limit function by clamping the COMP pin voltage to a maximum value, which limits the maximum peak current the device supplies. The device also implements a minimum COMP pin voltage clamp for improved transient response. When the COMP pin voltage is pushed low to the minimum clamp, such as during a load release event, turn-on of the high-side power switch is inhibited.